1. Field of the Invention
The present invention relates to an FM radio receiver, and particularly to a diversity FM radio receiver which receives using two antennas positioned separated by a distance.
2. Description of Related Art
Diversity FM radio receivers which have two separately provided antennas, such as one located at the front and the other located at the back of an automobile, and select and use one of the aforementioned antennas according to the condition of the reception are known from the prior art. The aforementioned diversity FM radio receiver, such as disclosed in JAS JOURNAL from page 3 to 9 issued in the November 1981, is able to reduce multipath-noise signal and skip-noise signal which are produced locally and have an adverse effect on FM signal received by one antenna, but no effect on FM signal received by the other antenna. However, the aforementioned diversity type FM radio receiver also responds to ignition-noise signal which is produced such as during the engine running period. Since the ignition-noise signal adversely effects simultaneously on FM signals received by the two antennas, the switching operation to change the use of antenna from one in the front to the other in the back, or vice versa, will not result in the reduction or deletion of the noise signal. In other words, with respect to the ignition-noise signal, the switching of the antenna merely results in unnecessary switching operation from a poor reception condition to a poor reception condition.
An FM receiver which can distinguish multipath-noise signal and skip-noise signal from ignition-noise signal is disclosed, for example, in Japanese Patent Laid-Open Publication No. 189820/1987 assigned to the same assignee as the present application. According to this FM receiver, counters are employed to count the number of occurrence of the noise signal from the two antennas individually, and then select the antenna with less noise signal reception condition. In this case, since the number of occurrence of the ignition-noise signal is the same in both antennas, it is possible to distinguish the aforementioned ignition-noise signal.
However, the problem is that the construction of the noise discriminator using a counter is complex, thus necessitating a larger chip surface area when designed into an integrated circuit.